<template>
  <div class="spec-preview">
    <img :src="imgObj.imgUrl"  />
    <div class="event" @mousemove="handler"></div>
    <div class="big" >
      <img :src="imgObj.imgUrl" ref="big" />
    </div>
    <div class="mask" ref="mask"></div>
  </div>
</template>

<script>
  export default {
    name: "Zoom",
    data(){
      return {
        currentIndex: 0,
      }
    },
    props:['skuImageList'],
    computed:{
      imgObj(){
        return this.skuImageList[this.currentIndex]||{}
      }
    },
    mounted(){
      // 全局事件总线，获取兄弟组件传过来的值
      this.$bus.$on("getIndex",(index)=>{
        this.currentIndex = index;
        // console.log(index)
      })
    },
    methods:{
      // 鼠标移动显示大图
      handler(event){
        // 获取蒙版元素
        let mask = this.$refs.mask;
        // 获取大图
        let big = this.$refs.big;
        //计算当鼠标移动时蒙版元素的定位left、top值 
        let left = event.offsetX-mask.offsetWidth/2
        let top = event.offsetY-mask.offsetHeight/2
        // 限制mask的活动范围
        // 这有个隐藏条件：大盒子的宽、高都是是马mask宽、高的两倍
        if(left<0){
          left = 0;
        }else if(left>mask.offsetWidth){
          left =  mask.offsetWidth;
        }
        if(top<0){
          top = 0;
        }else if(top>mask.offsetHeight){
          top = mask.offsetHeight
        }
        // mask的定位
        mask.style.left = left+"px";
        mask.style.top = top+"px";
        // 大图的定位
        big.style.left=-2*left+"px";
        big.style.top=-2*top+"px"
        
      },
    }
  }
</script>

<style lang="less">
  .spec-preview {
    position: relative;
    width: 400px;
    height: 400px;
    border: 1px solid #ccc;

    img {
      width: 100%;
      height: 100%;
    }

    .event {
      width: 100%;
      height: 100%;
      position: absolute;
      top: 0;
      left: 0;
      z-index: 998;
    }

    .mask {
      width: 50%;
      height: 50%;
      background-color: rgba(0, 255, 0, 0.3);
      position: absolute;
      left: 0;
      top: 0;
      display: none;
    }

    .big {
      width: 100%;
      height: 100%;
      position: absolute;
      top: -1px;
      left: 100%;
      border: 1px solid #aaa;
      overflow: hidden;
      z-index: 998;
      display: none;
      background: white;

      img {
        width: 200%;
        max-width: 200%;
        height: 200%;
        position: absolute;
        left: 0;
        top: 0;
      }
    }

    .event:hover~.mask,
    .event:hover~.big {
      display: block;
    }
  }
</style>